1. Field of the Invention
The present invention relates to the rechargeable battery arts and, more particularly to the manufacture of nickel zinc rechargeable battery cells.
2. Description of the Related Art
The advent of portable communication and computation devices that allow diverse mobile connectivity has fueled growth and innovation in the rechargeable battery field. Increased capacity and power has made possible the entry of rechargeable power sources in various fields including the power tool arena. Because power tools typically have large current demands, rechargeable power sources have necessarily evolved to accommodate rapid discharge characteristics. It can be appreciated that the present invention will also find use in applications other than power tools such as Uninterruptible Power Supplies (UPS), Electric Vehicles, and high demand consumer electronics—all of which require high carrying capacity and current discharging ability. Of course, the invention also applies to relatively lower discharge rate applications such as many mainstream consumer electronics applications.
Rechargeable power sources have various benefits over non-rechargeable sources. For example, the use of non-rechargeable power sources raises growing environmental concerns with respect to hazardous waste disposal and remediation. In light of the proliferation of portable devices, the number of non-rechargeable power sources needed to use those devices would be staggering. Rechargeable power sources allow a battery cell to be used repeatedly thus reducing the introduction of hazardous waste products into the environment. Further, rechargeable power sources allow the conservation of the metal and chemical resources that would otherwise be spent in non-rechargeable power sources. Finally, the use of rechargeable power sources encourages and expands continuing conservation efforts that are necessary for a growing population to embrace.
Although the benefits of rechargeable power sources are many, they are not without costs. In particular, the materials that comprise rechargeable power sources frequently pose a significant potential threat to the environment. Regional recycling agencies like the Northeast Recycling Council (NERC) are actively addressing the problems of disposal of rechargeable power sources. In a recent report by NERC, nine of the ten member states banned the disposal of lead acid batteries; six of the ten banned the disposal of Nickel/Cadmium batteries; and four of the ten banned the disposal of mercuric oxide batteries. The EPA has also weighed in and has recently closed feedback on industry wide practices for disposal of NiCad batteries stating,                NiCad batteries, commonly used in industrial and household appliances such as cordless phones, power tools and laptop computers, are one of a number of products that pose a potential environmental risk when disposed of incorrectly. The batteries contain both Nickel and Cadmium, the most toxic component, and can cause health problems when not disposed of properly. They are both heavy metals and can also adversely affect the environment during recycling and disposal.        
Because of the hazardous nature of some of the commonly used materials for conventional rechargeable power sources, it would be desirable to manufacture a rechargeable power source that reduces the quantity of any potentially hazardous materials. In particular, it would be desirable to find a substitute for the widely used nickel cadmium battery cell.
It has been found that rechargeable nickel zinc cells can provide a power-to-weight ratio comparable to and even exceeding nickel cadmium cells at a reasonable cost. However, nickel zinc battery technology has not been widely deployed for at least two reasons. First, it has been found to have a relatively limited cycle life. In other words, a given nickel zinc cell can only charge and discharge for a fraction of the cycles typically attained with a comparable nickel cadmium cell. This is due to zinc distribution and dendrite formation. Second, there has not been a suitable high volume manufacturing process developed for nickel zinc batteries.
It would be desirable to use, to the extent possible, existing manufacturing techniques to produce environmentally safer rechargeable power sources in order to leverage the existing manufacturing infrastructure rather than require a wholly new manufacturing base.